In the related art, as a bearing for a high-speed rotating body, a radial bearing which is used in a state of being attached so as to enclose a rotary shaft is known. As such a radial bearing, a radial foil bearing which includes a thin sheet-shaped top foil which forms a bearing surface, a back foil which elastically supports the top foil, and a cylindrical bearing housing which accommodates the top foil and the back foil is well known. As the back foil of the radial foil bearing, a bump foil in which a thin sheet is shaped into a wave shape and peak portions and valley portions are alternately formed is mainly used.
Generally, in the radial foil bearing, in order to prevent the top foil or the back foil from being detached from the bearing housing, one end portion (toe portion) of the top foil or the bump foil is directly fixed to the bearing housing or is indirectly fixed thereto via a spacer, using spot welding. Moreover, in order to perform mechanical fixation instead of welding, a structure in which one end portion of the top foil or the back foil (bump foil) is bent and the bent portion is engaged with an engagement groove formed in the bearing housing is also known (for example, Japanese Unexamined Patent Application, First Publication No. 2011-033176, and Japanese Unexamined Patent Application, First Publication No. 2011-017385). In this way, the one end portion is fixed using spot welding or engagement, and thus, the one end portion becomes a fixed end (fixed point) and the other end portion thereof becomes a free end.
In the radial foil bearing, when the rotary shaft which is supported by the bearing is rotated, a fluid lubricating film is formed between the top foil and the rotary shaft. At this time, a load acting on the rotary shaft is applied to the top foil through the fluid lubricating film, and thus, the top foil is pushed, and a width of each peak portion of the bump foil (back foil) which receives the load from the top foil is widened. Accordingly, the heights of the peak portions of the bump foil are decreased and bending of the top foil is accepted. That is, the heights of the peak portions of the bump foil are decreased, and thereby a space which can accommodate the bent portions of the top foil is formed. Accordingly, in the radial foil bearing, the shape of the bearing surface thereof is variable, and an appropriate fluid lubricating film is formed according to the load.
Moreover, as described above, when the bump foil receives the load and is deformed, the width of each of the peak portions is widened. At this time, sliding occurs between the bump foil and the top foil or between the bump foil and the bearing housing. Accordingly, when vibration (shaft vibration) occurs in the rotary shaft, vibration energy is dissipated by friction due to sliding, and vibration suppression effects are achieved.